Vocabulary

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texture: the look and feel of a rock

grains: what gives a rock its texture.

igneous rock: formed when magma hardens

sedimentary rock: formed when remains of plants and animals are pressed together.

metamorphic rock: formed when a rock is changed by pressure, heat or chemical reactions

Outline

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• How geologists classify rocks

  • rocks form mountains, hills, beaches, and valleys
    • earths crust is made of rock
  • rocks are made of mixtures of minerals and other materials
  • geologists collect and study rocks in order to classify them
  • geologists observe the rock's color texture and determine its mineral composition.

• Texture

  • texture is very useful when trying to identify a rock
  • examples of different kinds of textures are: smooth, glassy, rough, or chalky
  • a rocks grain gives the rock its texture

• grain size

  • grains in rock are large and easy to see
    • other rocks there to small to be seen they only can be seen under a microscope

• grain shape

  • rocks vary in shape

• grain pattern

  • the grain in rock often form patterns
  • examples of patterns are: flat and wavy layers

• no visible grain

  • some rocks have no grain

• mineral composition

  • geologist must look closely at rock to determine its mineral composition
  • they cut the rock very thin so the light can shine through the crystal
  • some of the test they use is: testing the rocks surface with acid or testing with a magnet

• origin

  • there are three major groups of rocks: igneous rock, sedimentary rock, and metamorphic rock